1. Field of the Invention
This invention relates to rotatory members for fixing, such as fixing rolls, etc. for fixing a toner image, onto a support member supporting the toner image and to a fixing device having the rotatory members. Particularly, it relates to a rotatory member for fixing having elastic layers constituted of a plurality of layers for prevention of swelling with a mold release or parting agent and a fixing device provided with the rotatory member.
2. Related Background Art
As a device for fixing toner image, the hot roll fixing device has been generally employed, and in such hot roll fixing device, it has been widely to prevent off-set phenomenon of toner by coating the fixing rolls with a mold release agent such as silicone-oil, etc.
Particularly, in a full-color image forming device which mixes toners with different plural colors, the fixing roll is required to have very high mold releasability, and for that purpose, the fixing roll is coated with a large amount of a mold release agent.
An example of such full-color image forming device is described below.
Formation of a latent image of an image on a photosensitive drum by color resolution signals of an original, formation of a toner image by coloration of the latent image with color toner, and transfer of the toner image onto a recording material are repeated one by one for each color. By doing so, for example, a full-color image is formed on a recording material, and a plurality of unfixed toner images formed on the recording material are fixed by an image fixing device arranged within the image forming device.
The image fixing device, as shown in FIG. 2, has a rotatory member for fixing, a fixing roller 1 which is generally made a roller shape and a pressurizing roller 2 opposed thereto, and is further equipped with a mold release agent coating means 3 for coating the fixing roller 1 with silicone oil as the mold release agent, and a cleaning means 4 for cleaning the fixing roller 1.
The fixing roller 1 comprises an elastic layer 6 comprising an HTV silicone rubber (high temperature vulcanization type silicone rubber) formed on a hollow core metal 5 generally made of aluminum as the substrate, an oil barrier layer F comprising a fluorine rubber on the elastic layer 6, and further an off-set prevention layer 7 comprising an RTV silicone rubber (room temperature vulcanization type silicone rubber) as the surface layer thereon, with the outer diameter being made, for example, 40 mm.
The pressurizing roller 2 comprises an elastic layer 9 comprising an HTV silicone rubber formed on a hollow core metal 8 made of aluminum, and a resin layer 10 such as of fluorine resin, etc. on the elastic layer 9, with the outer diameter being similarly made, for example, 40 mm.
Within the core metal 5 of the fixing roller 1 and the core metal 8 of the pressurizing roller 2, halogen heaters 11, which act as heating sources, are respectively arranged. The temperature of the pressurizing roller 2 :s detected with thermistors 12 in contact therewith to effect on-off control of the halogen heaters 11, whereby the temperatures of the fixing roller 1 and the pressurizing roller 2 are maintained constantly at about 170 .degree. C.
The mold release agent coating means 3 is adapted to aspirate the silicone oil 14 with a viscosity of 300 CS housed within the vessel 13 by means of the upper and lower supplying rollers 15A, 15B to coat the off-set prevention layer 7 of the fixing roller 1 with the oil. The amount of the silicone oil coated onto the off-set prevention layer 7 is controlled by the contact angle and the pressure of the oil amount controlling blade 16 in contact with the upper supplying roller 15A.
The cleaning means 4 removes the toner off-set onto the off-set prevention layer 7 of the fixing roller 1. Here, in the example shown, a web-shaped cleaning member is employed.
According to the fixing device as described above, a recording material P carrying a plurality of unfixed toner images T laminated thereon is conveyed in the direction of the arrow a by a conveying device (not shown), and the recording material P passes between the fixing roller 1 and the pressurizing roller 2 each rotated in the direction of the arrowhead b by a driving device (not shown) whereby the laminated toner images T can be mixed and thermally fixed on the recording material P to form a full-color image.
As mentioned above, the fixing roller 1 has an oil barrier layer F comprising a fluorine rubber, and therefore penetration of the silicone oil into the HTV silicone rubber layer 6 of the lower layer is prevented by the oil barrier layer F. Also, the silicone oil is held on the RTV silicone rubber layer 7 which is the upper layer of the barrier layer F, whereby high mold releasability can be obtained.
However, when a roller having an intermediate layer as such oil barrier layer is employed, stresses occur between the respective layers of the fixing roller through heat and pressure during fixing, and slippage with the pressurizing roller, etc., thus involving the problem that peeling occurs between the elastic layer of the lower layer and the oil barrier layer or between the oil barrier layer of the upper layer and the off-set prevention layer, whereby the roller cannot withstand prolonged usage.
The present invention has been accomplished in view of such problems.